President Bush warned defiant Republican senators yesterday that he will close down a CIA interrogation program that he credited with thwarting terrorist attacks if they pass a proposal regulating detention of enemy combatants, escalating a politically charged battle that has exposed divisions within his party.

An irritated Bush, raising his voice and gesturing sharply at a Rose Garden news conference, excoriated legislation passed by a Senate panel Thursday that is intended to conform U.S. detainee practices with the Geneva Conventions. Bush insisted on legislation more specifically defining what is banned so intelligence officers would not worry about being charged with war crimes.

"The professionals will not step up unless there's clarity in the law," Bush said. "So Congress has got a decision to make: Do you want the program to go forward or not? I strongly recommend that this program go forward in order for us to be able to protect America."

The president's threat to end the interrogation program seemed to make little impression on the Republican dissidents who have balked at his interpretation of the Geneva Conventions. Sens. John McCain (R-Ariz.) and Lindsey O. Graham (R-S.C.), two of four Republicans who voted against Bush's position on Thursday, again rejected his logic after the news conference, and a fifth Republican senator, Olympia J. Snowe (Maine), joined the rebellion against the president.

"Weakening the Geneva protections is not only unnecessary, but would set an example to other countries, with less respect for basic human rights, that they could issue their own legislative 'reinterpretations,' " McCain said in a written statement. "This puts our military personnel and others directly at risk in this and future wars."

The dispute over how the United States conducts its ongoing battle with international terrorists dominated a question-and-answer session with the president that touched on a variety of high-profile issues 53 days before the midterm elections. Bush lashed out at the United Nations for not moving more aggressively to stop genocide in Darfur, rejected what he called the "urban myth" that his administration has lost focus on finding Osama bin Laden, and acknowledged that spiraling violence in Iraq has frustrated his hopes to begin bringing U.S. troops home this year.

At a time when Bush hoped to be drawing distinctions with Democrats, though, he spent most of the conference arguing with fellow Republicans. As Congress tries to wrap up business to go home and campaign, Bush is pressing for legislation endorsing his leadership against terrorism, including warrantless surveillance of overseas telephone calls, military commissions to try enemy combatants and expansive rules permitting tough interrogations.

The most explosive debate centers on how the Geneva Conventions should apply to U.S. intelligence officers, who captured, held and questioned terrorism suspects in secret overseas CIA prisons for years until the last 14 detainees were transferred recently into military custody at Guantanamo Bay, Cuba.

The Supreme Court ruled in June that U.S. detainees fall under the Geneva Conventions, which require that wartime captives be "treated humanely" and ban "outrages upon personal dignity." Bush wants legislation interpreting the conventions as barring "cruel, inhuman or degrading" treatment, adopting language from a McCain-sponsored law on prisoners signed last year. The broader "personal dignity" phrases, he argues, are so vague that they leave interrogators open to prosecution for a wide variety of techniques.

McCain, Graham and Senate Armed Services Committee Chairman John W. Warner (R-Va.) have rejected the Bush approach as too narrow and as an invitation to other countries, including Iran, Syria and North Korea, to reinterpret the Geneva rules as they see fit if they ever hold U.S. soldiers. "What is being billed as 'clarifying' our treaty obligations will be seen as 'withdrawing' from the treaty obligations," Graham said. "It will set precedent which could come back to haunt us."

Another dispute centers on trials for terrorism suspects, who in the Bush proposal could under some circumstances be barred from the proceedings and not allowed to view classified evidence against them. The Republican legislation, passed by Warner's committee 15 to 9 on Thursday, would make it more difficult to introduce secret evidence.

Joining McCain and the other Republicans this week was former secretary of state Colin L. Powell, who wrote in a letter that reinterpreting the Geneva Conventions would encourage other countries to "doubt the moral basis of our fight against terrorism."

Bush bristled at the criticism from his former top diplomat yesterday, calling it "flawed logic" and accusing Powell of equating U.S. tactics with those of terrorists, even though Powell's letter made no such comparison. "It's unacceptable to think that there's any kind of comparison between the behavior of the United States of America and the action of Islamic extremists who kill innocent women and children," Bush said.

He likewise rejected the argument that nations such as Iran and North Korea would cite U.S. precedent in reinterpreting Geneva rules. "If the nations such as those you named adopted the standards within the Detainee Detention Act," Bush said, meaning the model for his preferred legislation, "the world would be better."

Asked twice if he would veto the McCain-backed bill, Bush avoided answering directly but repeated 11 times in the course of an hour that intelligence officials would not "go forward" with their interrogation program. "Were it not for this program, our intelligence community believes that al-Qaeda and its allies would have succeeded in launching another attack against the American homeland," he said.

In a nod to the harsh campaign rhetoric flying around Washington, Bush disavowed a statement by House Majority Leader John A. Boehner (R-Ohio), who suggested this week that Democrats care more about protecting terrorists than protecting Americans. "I wouldn't have exactly put it that way," Bush said. "But I do believe there's a difference of attitude."

Democrats, who have largely sat on the sidelines as Bush and Republicans battled this week, seized on the president's remarks yesterday. "Instead of picking fights with Colin Powell, John McCain and other military experts, President Bush should change course, do what the American people expect and finally give them the real security they deserve," said Senate Minority Leader Harry M. Reid (Nev.).

Sens. Edward M. Kennedy (D-Mass.) and Richard J. Durbin (D-Ill.) called for a Judiciary Committee investigation into whether military judge advocates general were pressured into writing a letter this week saying they "do not object" to two sensitive parts of the administration's legislation.

Officials who attended the meeting in question, in the office of Pentagon general counsel William J. Haynes II on Wednesday, said there was no pressure on the military lawyers to produce the letter, describing a robust discussion about how to word its contents. The lawyers initially drafted a letter saying they "support" the two sections but later settled on saying they "do not object" to them.

"None of us would have signed anything if we had not believed it and absolutely agreed with it," Col. Ronald M. Reed, counsel to the Joint Chiefs of Staff chairman, said yesterday. "The discussion was nothing out of the ordinary."

But late yesterday, Maj. Gen. Scott C. Black, the Army's judge advocate general, sent a new letter to McCain and other senators, saying "further redefinition" of the conventions "is unnecessary and could be seen as a weakening of our treaty obligations, rather than a reinforcement of the standards of treatment."